of laughter and of fury, nursing
his wounded wrist all the time like a mother with a sick baby.

Across the brown of the hard, pebbly desert there had been visible for
some time a single long, thin, yellow streak, extending north and south
as far as they could see. It was a band of sand not more than a few
hundred yards across, and rising at the highest to eight or ten feet.
But the prisoners were astonished to observe that the Arabs pointed at
this with an air of the utmost concern, and they halted when they came
to the edge of it like men upon the brink of an unfordable river. It
was very light, dusty sand, and every wandering breath of wind sent it
dancing into the air like a whirl of midges. The Emir Abderrahman tried
to force his camel into it, but the creature, after a step or two, stood
still and shivered with terror.

[Illustration: The creature, stood still p171]

The two chiefs talked for a little, and then the whole caravan trailed
off with their heads for the north, and the streak of sand upon their
left.

"What is it?" asked Belmont, who found the dragoman riding at his elbow.
"Why are we going out of our course?"

"Drift sand," Mansoor answered. "Every sometimes the wind bring it all
in one long place like that. To-morrow, if a wind comes, perhaps there
will not be one grain left, but all will be carried up into the air
again. An Arab will sometimes have to go fifty or a hundred miles to go
round a drift. Suppose he tries to cross, his camel breaks its legs, and
he himself is sucked in and swallowed."

"How long will this be?"

"No one can say."

"Well, Cochrane, it's all in our favour. The longer the chase the better
chance for the fresh camels!" and for the hundredth time he looked
back at the long, hard skyline behind them. There was the great, empty,
dun-coloured desert, but where the glint of steel or the twinkle of
white helmet for which he yearned?

And soon they cleared the obstacle in their front. It spindled away into
nothing, as a streak of dust would which has been blown across an empty
room. It was curious to see that when it was so narrow that one could
almost jump it, the Arabs would still go for many hundreds of yards
rather than risk the crossing. Then, with good, hard country before them
once more, the tired beasts were whipped up, and they ambled on with a
double-jointed jog-trot, which set the prisoners nodding and bowing in
grotesque and ludicrous misery. It was fun at first, and they smiled
at each other, but soon the fun had become tragedy as the terrible
camel-ache seized them by spine and waist, with its deep, dull throb,
which rises gradually to a splitting agony.

"Lean back, and hold your saddle behind," said the Colonel. "There,
you'll find that will ease the strain." He took the puggaree from his
hat, and, tying the ends together, he slung it over her front pommel.
"Put your foot in the loop," said he. "It will steady you like a
stirrup."

The relief was instant, so Stephens did the same for Sadie. But
presently one of the weary doora camels came down with a crash, its
limbs starred out as if it had split asunder, and the caravan had to
come down to its old sober gait.

"Is this another belt of drift sand?" asked the Colonel, presently.

"No, it's white," said Belmont. "Here, Mansoor, what is that in front of
us?"

But the dragoman shook his head.

"I don't know what it is, sir. I never saw the same thing before."

Right across the desert, from north to south, there was drawn a white
line, as straight and clear as if it had been slashed with chalk across
a brown table. It was very thin, but it extended without a break from
horizon to horizon. Tippy Tilly said something to the dragoman.